Such instruments are relatively expensive and must therefore be capable of being used several times. Between two uses, they must be cleaned thoroughly and then decontaminated or sterilized. Cleaning the insides of the ducts turns out to be very difficult and requires a device of the above-specified type to be used like a bottle-brush or a ram-rod.
The radial size of the device must be small enough to enable it to be inserted in a duct whose diameter is generally small, e.g. of the order of 1 mm to 20 mm. In addition, the device must be sufficiently flexible to be capable of passing round any bends there may be in the duct, and in particular it must be capable of thoroughly cleaning any fork ones. In spite of its small radial size and its flexibility, the device must be relatively stiff axially, i.e. it must be strong enough to be pushed and pulled so as to be capable of being inserted along the entire length of the duct, which may as much as 1 or 2 meters, by being pushed in via one of the ends of the duct.
U.S. Pat. No. 5,168,593 shows a cleaning device in which the brush is connected to the cylindrical support element via a helical spring. More precisely, the spine of the brush is fixed to a first end of the spring, and the other end of the spring is fixed to the elongate cylindrical element.
That serves to make a flexible connection between the brush and the cylindrical element.
Unfortunately, those dispositions confer no flexibility to the brush itself.
It is not possible to impart radial flexibility only to the bristle-supporting spine of the brush without also making it axially flexible.
To enable the brush to pass through sharp bend zones of ducts, a first solution consists in providing it with a flexible spine. Unfortunately, axial flexibility impedes insertion of the brush into ducts and directly degrades its effectiveness. In any event, the mere fact of providing a long brush with a flexible spine is not satisfactory insofar as such a spine is not itself strong enough, so it breaks after being flexed repeatedly.
A second solution consists in making a brush that is very short (of length substantially equal to its diameter), and that is provided with a rigid spine, this relies on the fact that given the short length of the brush there is no need for its spine to bend significantly, even in zones of high curvature. Such a brush suffers from the drawback of being too short to clean certain particularly dirty ducts properly.
Thus, merely giving the device local flexibility in the connection zone between the brush and the supporting cylindrical element (itself sufficiently flexible radially and sufficiently stiff axially) does not suffice to ensure that the device is reliable.